pang-chi hsu, chih-hua tsou department of earth science, ntnu, taiwan
DESCRIPTION
Multi-scale Interaction between ENSO and Large-scale Circulation along the Tropical Storm Track. Pang-chi Hsu, Chih-Hua Tsou Department of Earth Science, NTNU, Taiwan. Outline. Motivation Data and Model Description Numerical Experiments Simulated Results Summary. Motivation. - PowerPoint PPT PresentationTRANSCRIPT
Pang-chi Hsu, Chih-Hua Tsou
Department of Earth Science,
NTNU, Taiwan
Motivation
Data and Model
Description
Numerical Experiments
Simulated Results
Summary
Outline
Which one plays the active role ? ENSO-related warm SST anomaly, the enhancement a
nd eastward-extension of low-level westerly, monsoon
trough beneficial for TS formation and development al
l occur simultaneously.
Eddy energetics
Numerical experiment
Motivation
Eddy energy budget equations
Zonal mean Eddy Less study
Time mean Transient Eddy
General circulationExtratropical cyclones
Lorenz (1955)
Kung (1966)
﹕
Hu et al. (2004)
General circulation
Oort (1964)
No calculation
Synoptic disturbanceLau and Lau (1992)
MJO-TD type eddyMaloney and Dickson (2003)
By 3-D EKE budget eq.
& 2-D EAPE budget eq.
3-D EKE/EAPEdiagnosis
Walker Circulation
Data
NCEP / DOE (NCEP R2) : 144 × 73 × 17
NCEP monthly SST : 180 × 90
JTWC 6-hourly best track
Based on Wang and Chan (2002), the TS activity over
the WNP is closely related to Nino3.4 SSTA in
summer.
The classifications of ENSO are stratified by JAS
SSTA in Nino3.4 region into
Warm years (SSTA ≥ 0.8 S.D.): 1982, 1987, 1991, 1997
Cold years (SSTA ≤ -0.8 S.D.): 1981, 1985, 1988, 1998
ECHAM4.6 : MPI, Germany (Roecknet et al. 1996)
High resolution: T106 (320×160) L19
6-hourly output for TS identification and trajectory
Forced with observed monthly SST and sea-ice (AMIP run) f
or 1979-1999
Model Description
Vitart et al. (1997) and Knutson et al. (2007)
ECHAM 4.6 T106 control run
Numerical Experiments
Expt SST boundary condition
CTL Globally observed SST
noTPO Observed SST everywhere except Central-Eastern
Pacific (100ºE-80ºW, 15ºS-15ºN)
Two numerical experiments are designed to clarify whether the ENSO-related SST anomaly
plays an active role to the interanuual variations of large-scale circulations and TS activity.
Motivation
Data and Model
Description
Numerical Experiments
Simulated Results
Summary
Outline
Overestimate (underestimate) the response of heating (cooling ) effect
TS frequency has eastward bias
Camargo et al. (2005)
Obs
CTL
<Warm minus Cold>
No warming and cooling
no westerly jet
A-C wavetrain still exists
but shifts northeastward
ENSO-related SST anomalies
Strong westerly
Cyclonic shear (monsoon trough)
favorable environment for TS activity
insignificant interannual TS variation
Ratio (Warm years) TS activity
indices JTWC CTL noTPO
Number 1.10 ( 54 ) 1.80 ( 54 ) 1.15 ( 39 )
ACE (104 m2/s2) 2.17 (55.14) 1.51 (15.61) 0.93 (9.93)
Lifespan (day) 1.48 (9.75) 0.93 (8.01) 1.03 (8.72)
Max wind (m/s) 1.27 (47.57) 0.98 (21.30) 0.98 (21.46)
The TS number and life span of TS during warm years are similar to JTWC,
but the intensity of simulated TS is too weak (Bengtsson et al. 2007).
ENSO-related SST anomalies play an active role in modulating the TS activit
y over the WNP.
WHY?
Eddy energetics along the TS track (obs)
MKE to EKE EAPE to EKE
Enhanced eddy barotropic and baroclinic energy conversion might be benefici
al for the southeastward extension of the TS formation region and the intensificat
ion of the TS during warm events.
The eddy baroclinic energy conversion plays a significant role in maintaining th
e subsequent development of eddies.
Less EKE converted from EAPE
Insufficient EAPE generation and eddy baroclinic energy conversion
Summary
The results of numerical experiments support that the El Nino-r
elated anomalous SST forcing plays an active role in setting the
favorable large-scale environments for the formation and early-
development of transient eddies including TS over the WNP.
The inadequate simulation of eddy diabatic heating and eddy b
aroclinic processes which might be resulted from insufficient res
olution would lead to the underestimate of TS intensity in ECH
AM4 T106.
Thanks for your attention